The present disclosure generally relates to systems and processes for CO2 capture entrained in flue gases. More particularly, the present disclosure relates to the efficient recovery of ammonia from the ammonium sulfate byproduct of the chilled ammonia process in the carbon capture system.
Most of the energy used in the world is derived from the combustion of carbon and hydrogen-containing fuels such as coal, oil and natural gas. In addition to carbon and hydrogen, these fuels contain oxygen, moisture and undesirable contaminants such as SOx, e.g., SO2, SO3 and the like, NOx, mercury, chlorine, and other trace elements. Awareness regarding the damaging effects of the contaminants released during combustion triggers the enforcement of ever more stringent limits on emissions from power plants, refineries and other industrial processes. There is an increased pressure on operators of such plants to achieve near zero emission of contaminants
Numerous processes and systems have been developed in response to the desire to achieve near zero emission of contaminants. Systems and processes include, but are not limited to desulfurization systems (known as wet flue gas desulfurization systems (“WFGD”) and dry flue gas desulfurization systems (“DFGD”)), particulate filters (including, for example, bag houses, particulate collectors, and the like), as well as the use of one or more sorbents that absorb contaminants from the flue gas. Examples of sorbents include, but are not limited to, activated carbon, ammonia, limestone, and the like.
It has been shown that ammonia, as well as amine solutions, efficiently removes CO2, as well as other contaminants, such as sulfur dioxide (SO2) and hydrogen chloride (HCl), from a flue gas stream. In one particular application, CO2 is absorbed in an ammoniated solution at temperatures lower than the exit temperature from the flue gas desulfurization system, for example, between 0 and 30 degrees Celsius (0°-30° C.). The SOx contaminants, e.g., SO2, SO3, remaining in the flue gas coming from the wet flue gas desulfurization (WFDS) and/or dry flue gas desulfurization (DFGD) is often captured by ammonia to produce an ammonium sulfate bleed stream. Ammonium sulfate is also produced in the ammonia reduction stages of the carbon capture from the exhaust flue gas Ammonium sulfate can be used as a commercial fertilizer, but processing of the ammonium sulfate byproduct can be energy and capital cost intensive. In some cases, the use of crystallization, evaporation, agglomeration equipment is needed in order to produce the fertilizer product for commercial use. In addition, a large area for silos\bins for indoor storage of the ammonium sulfate byproduct may be needed on-site to insure plant availability. In addition, trace metals may be present in the ammonium sulfate stream that may require further treatment or disposal of the ammonium sulfate stream as a hazardous waste. For example, for CO2 capture systems which use amine solutions, sulfur compounds present in the flue gas will react with the amine reagent and render it useless. The sulfonated amine must then be discarded and replenished with fresh reagent. The result is higher operating costs and capital costs because of the larger equipment needed to account for sulfur and the higher reagent make-up rates.
An alternative approach to the handling and/or disposal of the ammonium sulfate byproduct from the carbon capture system utilizes a lime boil process, in which the ammonium sulfate is converted to calcium sulfate and the ammonia is recovered. This alternative process, however, uses a significant amount of heat in order to convert the ammonium sulfate and recover ammonia.
Accordingly, there is a need in the art for improved systems and processes for handling the ammonium sulfate byproduct and recovering the ammonia in carbon capture systems.